Earth formations may be used for various purposes such as hydrocarbon production, geothermal production, and carbon dioxide sequestration. In order to efficiently use an earth formation, the formation is characterized by performing measurements of many different properties using one or more tools conveyed through a borehole penetrating the formation. One category of tools is acoustic tools that use sound waves to perform various measurements such as imaging a wall of the borehole or measuring rugosity of the borehole. An acoustic tool includes one or more acoustic transducers that convert electrical energy into sound wave energy to transmit an acoustic signal or convert sound wave energy into electrical energy to receive an acoustic signal. Some transducers may be used to both transmit and receive an acoustic signal.
One type of acoustic transducer is based on piezoelectric material technology. Unfortunately, there are some disadvantages to using piezoelectric transducers downhole. Due to the characteristics of piezoelectric materials, piezoelectric transducers require a large size in comparison to the space available in a tool sized to fit in a borehole that is typically inches in diameter. Consequently, the number of piezoelectric transducers that may be used in a tool may be constrained leading to lower accuracy or resolution than if more transducers were used in the tool. Another disadvantage to using piezoelectric transducers downhole, where temperatures can be as high as 300° C., is that piezoelectric materials start to depole at temperatures above 150° C. and their performance is degraded significantly during extended operation at high temperatures. Hence, it would be well received in the drilling industry if smaller acoustic transducers that could operate at high downhole temperatures would be developed.